HEMT and method of fabricating the same

ABSTRACT

An HEMT includes a first III-V compound layer. A second III-V compound layer is disposed on the first III-V compound layer. The composition of the first III-V compound layer is different from the composition of the second III-V compound layer. A third III-V compound layer is disposed on the second III-V compound layer. The first III-V compound layer and the third III-V compound layer are composed of the same group III-V elements. The third III-V compound layer includes a body and numerous finger parts. Each of the finger parts is connected to the body. All finger parts are parallel to each other and do not contact each other. A source electrode, a drain electrode and a gate electrode are disposed on the first III-V compound layer.

BACKGROUND OF THE INVENTION 1. Field of the Invention

The present invention relates to a high electron mobility transistor(HEMT) and a fabricating method of the HEMT and more particularly to anHEMT with finger parts extending from the gate and method of fabricatingthe same.

2. Description of the Prior Art

Due to their semiconductor characteristics, III-V semiconductorcompounds may be applied in many kinds of integrated circuit devices,such as high power field effect transistors, high frequency transistors,or high electron mobility transistors (HEMTs). In the high electronmobility transistor, two semiconductor materials with differentband-gaps are combined and a heterojunction is formed at the junctionbetween the semiconductor materials as a channel for carriers. In recentyears, gallium nitride (GaN) based materials have been applied in highpower and high frequency products because of their properties of widerband-gap and high saturation velocity.

A two-dimensional electron gas (2DEG) may be generated by thepiezoelectric property of the GaN-based materials, and the switchingvelocity may be enhanced because of the higher electron velocity and thehigher electron density of the 2DEG.

Regarding punch-through voltage of HEMTs, the punch-through of HEMTsmainly occurs under the sidewall of the gate which is close to thedrain. Therefore, in order to improve the operating efficiency of HEMTs,punch-through voltage has to be increased.

SUMMARY OF THE INVENTION

In light of the above, the present invention provides an HEMT with agate having finger parts to increase the punch-through voltage of theHEMT.

According to a preferred embodiment of the present invention, an HEMTincludes a first III-V compound layer and a second III-V compound layerdisposed on the first III-V compound layer, wherein a composition of thefirst III-V compound layer is different from a composition of the secondIII-V compound layer. A third III-V compound layer is disposed on thesecond III-V compound layer, wherein the third III-V compound layerincludes a body and a plurality finger parts, each of the finger partsis connected to the body, all finger parts are parallel to each otherand do not contact each other. A source electrode is disposed at oneside of the body and contacts the first III-V compound layer. A drainelectrode is disposed at another side of the body and contacts the firstIII-V compound layer. A gate electrode is disposed directly on the body.

According to another preferred embodiment of the present invention, afabricating method of an HEMT includes forming a first III-V compoundlayer and a second III-V compound layer, wherein the second III-Vcompound layer is disposed on the first III-V compound layer, and acomposition of the first III-V compound layer is different from acomposition of the second III-V compound layer. Next, a third III-Vcompound layer is formed to be disposed on the second III-V compoundlayer, wherein the third III-V compound layer includes a body andnumerous finger parts, each of the finger parts is connected to thebody, all finger parts are parallel to each other and do not contacteach other. Finally, a source electrode, a drain electrode and a gateelectrode are formed, wherein the source electrode is disposed at oneside of the body, the drain electrode is disposed at another side of thebody and the gate electrode is disposed directly on the body.

These and other objectives of the present invention will no doubt becomeobvious to those of ordinary skill in the art after reading thefollowing detailed description of the preferred embodiment that isillustrated in the various figures and drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 depicts a three-dimensional view of an HEMT according to a firstpreferred embodiment of the present invention.

FIG. 2 depicts a top view of an HEMT according to a first preferredembodiment of the present invention.

FIG. 3 depicts a top view of an HEMT according to a varied type of thefirst preferred embodiment of the present invention.

FIG. 4 depicts a top view of an HEMT according to another varied type ofthe first preferred embodiment of the present invention.

FIG. 5 depicts a three-dimensional view of an HEMT according to a secondpreferred embodiment of the present invention.

FIG. 6 depicts a top view of an HEMT according to a second preferredembodiment of the present invention.

FIG. 7 depicts a top view of an HEMT according to a varied type of thesecond preferred embodiment of the present invention.

FIG. 8 depicts a top view of an HEMT according to another varied type ofthe second preferred embodiment of the present invention.

FIG. 9 and FIG. 10 depict a fabricating method of an HEMT with both abody and finger parts having P-type dopants.

FIG. 11 and FIG. 12 depict another fabricating method of an HEMT withboth a body and finger parts having P-type dopants.

FIG. 13 and FIG. 14 depict a fabricating method of an HEMT with a bodyhaving P-type dopants and finger parts undoped according to a preferredembodiment of the present invention.

FIG. 15 and FIG. 16 depict a fabricating method of an HEMT with a bodyhaving P-type dopants and finger parts undoped according to anotherpreferred embodiment of the present invention.

DETAILED DESCRIPTION

FIG. 1 depicts a three-dimensional view of an HEMT according to a firstpreferred embodiment of the present invention. FIG. 2 depicts a top viewof an HEMT according to a first preferred embodiment of the presentinvention, wherein in order to show a third III-V compound layerclearly, a source electrode, a drain electrode and a gate electrode areomitted.

Please refer to FIG. 1 and FIG. 2 . An HEMT 100 includes a substrate 10.A first III-V compound layer 12 is disposed on the substrate 10. Asecond III-V compound layer 14 is disposed on the first III-V compoundlayer 12. The composition of the first III-V compound layer 12 isdifferent from the composition of the second III-V compound layer 14. Athird III-V compound layer 16 is disposed on the second III-V compoundlayer 14. The first III-V compound layer 12 and the third III-V compoundlayer 16 can be composed of the same group III-V elements or be composedof different group III-V elements. The third III-V compound layer 16includes a body 16 a and numerous finger parts 16 b. Each of the fingerparts 16 b is connected to the body 16 a. All finger parts 16 b areparallel to each other and do not contact each other. Dotted lines areapplied in FIG. 2 to define the positions of the body 16 a and thefinger parts 16 b, however, the dotted lines are not really on theelements. A source electrode 18 is disposed at one side of the body 16 aand contacts the first III-V compound layer 12. A drain electrode 20 isdisposed at another side of the body 16 a and contacts the first III-Vcompound layer 12. A gate electrode 22 is disposed directly on the body16 a. The body 16 a serves as a gate of the HEMT 100.

According to a preferred embodiment of the present invention, the firstIII-V compound layer 12 and the third III-V compound layer 16 can begallium nitride or aluminum gallium nitride. But the first III-Vcompound layer 12 is an undoped III-V compound layer, and the thirdIII-V compound layer 16 is a P-type III-V compound layer. For example,the first III-V compound layer 12 can be an undoped gallium nitride. Thethird III-V compound layer 16 can be P-type gallium nitride. Moreover,there are no N-type dopants within the third III-V compound layer 16.That is, there are no N-type dopants within the body 16 a and fingerparts 16 b. The second III-V compound layer 14 includes aluminum galliumnitride, aluminum indium nitride, aluminum indium gallium nitride oraluminum indium. In this embodiment, the second III-V compound layer 14is undoped aluminum gallium nitride. The source electrode 18, the drainelectrode 20 and the gate electrode 22 can respectively include Au, W,Co, Ni, Ti, Mo, Cu, Al, Ta, Pd, Pt or a chemical composition, acomposite layer or an alloy including a combination of aforesaidmaterials. The substrate 10 includes silicon substrate, a germaniumsubstrate, a gallium arsenide substrate, a silicon germanium substrate,a indium phosphide substrate, a gallium nitride substrate, a siliconcarbide substrate or a silicon on insulator substrate. The HEMT 100 is anormally off transistor. When the HEMT 100 is turned on, 2DEG 24 isformed in the interface between the first III-V compound layer 12 andthe second III-V compound layer 14.

Moreover, the finger parts 16 b of the third III-V compound layer 16 aredisposed between the body 16 a and the drain electrode 20. The fingerparts 16 b extend along a direction which moves away from the body 16 a.In this way, the third III-V compound layer 16 forms a comb profile.Although in the first preferred embodiment, the number of the fingerparts are 4, however, the number of the finger parts 16 b can beadjusted based on different product requirements. It is noteworthy thatthe electric field of the interface between the first III-V compoundlayer 12 and the second III-V compound layer 14 covered by the fingerparts 16 b becomes uniform. The uniform electric field can increase thewithstand voltage of the HEMT 100. That is, the punch-through voltage ofthe HEMT 100 is increased. On the other hand, if the third III-Vcompound layer 16 does not include the finger parts 16 b, and onlyincludes the body 16 a, large electric field will accumulate below thecorner of the body 16 a. More specifically speaking, a large amount ofelectrons will accumulate at the corner A of the body 16 a which isclose to the drain electrode 20. Under this circumstance, currentleakage is occurred easily, and the punch-through voltage of the HEMT100 becomes lower.

Furthermore, the finger parts 16 b extending from the body 16 a do notconnect to each other. In this way, a gap is formed between two adjacentfinger parts 16 b; therefore, a part of the interface between the firstIII-V compound layer 12 and the second III-V compound layer 14 disposedbetween the body 16 a and the drain electrode 20 is not covered by thefinger parts 16 b, and 2DEG 24 can be formed within the interface. Underthis circumstance, when the HEMT 100 is turned on, 2DEG 24 can flow inthe interface not covered by the finger parts 16 b. On the contrary, ifthe interface between the first III-V compound layer 12 and the secondIII-V compound layer 14 is covered by a continuous third III-V compoundlayer, 2DEG 24 can not be formed at the interface. In this way, when theHEMT 100 is turned on, large voltage is needed in order to form achannel. In other words, an HEMT with a continuous third III-V compoundlayer covering between the body 16 a and the drain electrode 20 has ahigher Ron (on-state resistance) comparing to the HEMT 100 with fingerparts 16 b covering between the body 16 a and the drain electrode 20.

FIG. 3 depicts a top view of an HEMT according to a varied type of thefirst preferred embodiment of the present invention. FIG. 4 depicts atop view of an HEMT according to another varied type of the firstpreferred embodiment of the present invention. In order to show a thirdIII-V compound layer clearly, a source electrode, a drain electrode anda gate electrode are omitted. Elements which are substantially the sameas those in the first preferred embodiment are denoted by the samereference numerals; an accompanying explanation is therefore omitted.

As mentioned above, the third III-V compound layer 16 is formed by abody 16 a and numerous finger parts 16 b. FIG. 2 is exemplified by thefinger parts 16 b extending toward the drain electrode 20, which meansthat the finger parts 16 b are only disposed between the body 16 a andthe drain electrode 20, but not limited to this. As shown in FIG. 3 ,the finger parts 16 b extend toward the source electrode 18, and thefinger parts 16 b are only disposed between the body 16 a and the sourceelectrode 18. As shown in FIG. 4 , the finger parts 16 b extend towarddrain electrode 20 and the source electrode 18.

FIG. 5 depicts a three-dimensional view of an HEMT according to a secondpreferred embodiment of the present invention. FIG. 6 depicts a top viewof an HEMT according to a second preferred embodiment of the presentinvention, wherein in order to show a third III-V compound layerclearly, a source electrode, a drain electrode and a gate electrode areomitted. Elements which are substantially the same as those in the firstpreferred embodiment are denoted by the same reference numerals; anaccompanying explanation is therefore omitted.

The difference between the first preferred embodiment and the and thesecond preferred embodiment is that the third III-V compound layer 16 inthe second preferred embodiment is formed by a P-type III-V compoundlayer and an undoped III-V compound layer. More specifically speaking,the body 16 a in the second preferred embodiment is formed by a P-typeIII-V compound layer, and the finger parts 16 c in the second preferredembodiment is formed by an undoped III-V compound layer. Furthermore,the III-V compound layer in the body 16 a and in the finger part 16 care composed of the same group III-V elements. For example, the body 16a can be a P-type gallium nitride, and the finger parts 16 c can be anundoped gallium nitride. Moreover, there are no N-type dopants in thebody 16 a and the finger parts 16 c. Other elements in the secondpreferred embodiment are the same as those in the first preferredembodiment, an accompanying explanation is therefore omitted. No matterthe finger parts 16 b/16 c are formed by a P-type III-V compound layeror an undoped III-V compound layer, the HEMTs 100/200 have highwithstand voltages and a low Ron. The difference between the HEMTs100/200 is that when the finger parts 16 b formed by a P-type III-Vcompound layer, 2DEG 24 of the HEMT 100 has higher current density, whenthe finger parts 16 c formed by a undoped III-V compound layer, 2DEG 24of the HEMT 200 has lower current density.

FIG. 7 depicts a top view of an HEMT according to a varied type of thesecond preferred embodiment of the present invention. FIG. 8 depicts atop view of an HEMT according to another varied type of the secondpreferred embodiment of the present invention. In order to show a thirdIII-V compound layer clearly, a source electrode, a drain electrode anda gate electrode are omitted. Elements which are substantially the sameas those in the first preferred embodiment are denoted by the samereference numerals; an accompanying explanation is therefore omitted.

FIG. 6 is exemplified by the finger parts 16 c extending toward thedrain electrode 20, which means that the finger parts 16 c are onlydisposed between the body 16 a and the drain electrode 20, but notlimited to this. As shown in FIG. 7 , the finger parts 16 c extendtoward the source electrode 18, and the finger parts 16 c are onlydisposed between the body 16 a and the source electrode 18. As shown inFIG. 8 , the finger parts 16 c extend toward drain electrode 20 and thesource electrode 18.

The following paragraphs illustrate numerous methods of fabricating theHEMT in the present invention, however, the fabricating methods of theHEMT in the present invention are not limited by those methods. Othersuitable fabricating methods could be used in the present invention.FIG. 9 and FIG. 10 depict a fabricating method of an HEMT with both abody and finger parts having P-type dopants. FIG. 11 and FIG. 12 depictanother fabricating method of an HEMT with both a body and finger partshaving P-type dopants. Elements which are substantially the same asthose in the first preferred embodiment are denoted by the samereference numerals; an accompanying explanation is therefore omitted.

As shown in FIG. 9 , a substrate 10 is provided. Then, a first III-Vcompound layer 12 and a second III-V compound layer 14 are formed insequence to cover the substrate 10. Later, a third III-V compound layer16 is formed to be disposed on the second III-V compound layer.According to a preferred embodiment of the present invention, the firstIII-V compound layer 12 and the third III-V compound layer 16 aregallium nitride. But the first III-V compound layer 12 is undopedgallium nitride. The third III-V compound layer 16 is P-type galliumnitride. The second III-V compound layer 14 is undoped aluminum galliumnitride.

As shown in FIG. 10 , a lithographic process is performed to pattern thethird III-V compound layer 16 to form a body 16 a and numerous fingerparts 16 b. The finger parts 16 b extend from the body 16 a. Next, asshown in FIG. 1 , a source electrode 18 and a drain electrode 20 areformed simultaneously at two sides of the third III-V compound layer 16.The source electrode 18 and the drain electrode 20 contact the firstIII-V compound layer 12 and the second III-V compound layer 14. Next, agate electrode 22 is formed to contact the body 16 a. At this point, anHEMT 100 of the present invention is completed.

According to another fabricating method, as shown in FIG. 11 , asubstrate 10 is provided. Later, a first III-V compound layer 12 and asecond III-V compound layer 14 are formed in sequence to cover thesubstrate 10. Then, a first protective layer 26 is formed to cover thesecond III-V compound layer 14. Subsequently, the first protective layer26 is patterned to form a first opening 28 which defines predeterminedpositions of a third III-V compound layer 16. Next, a third III-Vcompound layer 16 is formed to fill up the first opening 28, and thethird III-V compound layer 16 is framed by the first opening 28 to formthe body 16 a and finger parts 16 b. As shown in FIG. 12 , the firstprotective layer 26 is patterned again to form two second openings 30exposing the first III-V compound layer 12. The two openings 30 definepredetermined positions of a source electrode 18 and a drain electrode20. Next, the source electrode 18 and the drain electrode 20 are formedto fill in each of the second openings 30. After that, a secondprotective layer 32 is formed to cover the first protective layer 26,the third III-V compound layer 16, the source electrode 18 and the drainelectrode 20. Later, the second protective layer 32 is etched to formthree third openings 36 within the second protective layer 32. The body16 a, the source electrode 18 and the drain 20 are exposed through thethird openings 36. Later, the gate electrode 22 is formed to fill in oneof the third openings 36 and the gate electrode 22 contacts the body 16a. The first protective layer 26 and the second protective layer 32 maybe silicon nitride or aluminum nitride. Now, an HEMT 300 of the presentinvention is completed.

FIG. 13 and FIG. 14 depict a fabricating method of an HEMT with a bodyhaving P-type dopants and finger parts undoped according to a preferredembodiment of the present invention. FIG. 15 and FIG. 16 depict afabricating method of an HEMT with a body having P-type dopants andfinger parts undoped according to another preferred embodiment of thepresent invention. Elements which are substantially the same as those inthe first preferred embodiment are denoted by the same referencenumerals; an accompanying explanation is therefore omitted.

As shown in FIG. 13 , a substrate 10 is provided. Later, a first III-Vcompound layer 12 and a second III-V compound layer 14 and a P-typeIII-V compound layer are formed in sequence to cover the substrate 10.According to a preferred embodiment of the present invention, the firstIII-V compound layer 12 is undoped gallium nitride. The P-type III-Vcompound layer is P-type gallium nitride. The second III-V compoundlayer 14 is undoped aluminum gallium nitride. Later, a mask layer 38 isformed to cover the P-type III-V compound layer. Next, the mask layer 38is patterned. After that, the P-type gallium nitride is patterned toform a body 16 a by taking the mask layer 38 as a mask. As shown in FIG.14 , an undoped III-V compound layer 40 is formed to cover the secondIII-V compound layer 14. As shown in FIG. 5 , after removing the masklayer 38, the undoped III-V compound layer 40 is patterned to formnumerous finger parts 16 c. Now, the undoped III-V compound layer 40 andthe P-type III-V compound layer form a third III-V compound layer 16.Next, a source electrode 18, a drain electrode 20 and a gate electrode22 are formed. The source electrode 18 and the drain electrode 20contact the first III-V compound layer 12. The gate electrode 22contacts the body 16 a.

According to another fabricating process in continuous from FIG. 13 ,after forming the body 16 a, as shown in FIG. 15 , the mask layer 38 isremoved. Later, a protective layer 42 is formed to cover the body 16 aand the second III-V compound layer 14. The protective layer 42 ispatterned to form a first opening 44 which defines predeterminedpositions of numerous finger parts 16 c. The second III-V compound layer14 is exposed from the first opening 44. Next, an undoped III-V compoundlayer is formed to fill up the first opening 44 to form the finger parts16 c. As shown in FIG. 16 , the protective layer 42 is patterned to formnumerous second openings 46 respectively defining a predeterminedposition of a source electrode 18, a drain electrode 20 and a gateelectrode 22. Subsequently, the source electrode 18, the drain electrode20 and the gate electrode 22 are formed to fill in each of the secondopenings 46. The source electrode 18 and the drain electrode 20 contactthe first III-V compound layer 12, and the gate electrode 22 contactsthe body 16 a. Now, an HEMT 400 of the present invention is completed.

The normally-off HEMT of the present invention has numerous finger partsextend from the body. In this way, the electric field of the interfacebetween the first III-V compound layer and the second III-V compoundlayer covered by the finger parts become uniform, and a withstandvoltage of the HEMT is increased.

Those skilled in the art will readily observe that numerousmodifications and alterations of the device and method may be made whileretaining the teachings of the invention. Accordingly, the abovedisclosure should be construed as limited only by the metes and boundsof the appended claims.

What is claimed is:
 1. A fabricating method of a high electron mobilitytransistor (HEMT), comprising: forming a first III-V compound layer anda second III-V compound layer, wherein the second III-V compound layeris disposed on the first III-V compound layer, and a composition of thefirst III-V compound layer is different from a composition of the secondIII-V compound layer; forming a third III-V compound layer disposed onthe second III-V compound layer, wherein the third III-V compound layercomprises a body and a plurality of finger parts, each of the fingerparts is connected to the body, all finger parts are parallel to eachother; and forming a source electrode, a drain electrode and a gateelectrode, wherein the source electrode is disposed at one side of thebody, the drain electrode is disposed at another side of the body andthe gate electrode is disposed directly on the body, wherein steps offorming the third III-V compound layer comprises: before forming thethird III-V compound layer, forming a first protective layer coveringthe second III-V compound layer; patterning the first protective layerto form a first opening which defines predetermined positions of thebody and the plurality of finger parts, wherein the second III-Vcompound layer is exposed form the first opening; forming a P-type III-Vcompound layer filling up the first opening to form the body and theplurality of finger parts; after forming the body and the plurality offinger parts, patterning the first protective layer to form two secondopenings which define predetermined positions of the source electrodeand the drain electrode; forming the source electrode and the drainelectrode to fill in each of the second openings, wherein the sourceelectrode and the drain electrode contact the first III-V compoundlayer; forming a second protective layer covering the first protectivelayer, the body, the plurality of finger parts, the source electrode,and the drain electrode; patterning the second protective layer to formthree third openings within the second protective layer, the thirdopenings respectively defining a predetermined position of the gateelectrode, exposing the source electrode and exposing the drainelectrode; and forming the gate electrode to fill in one of the thirdopenings and contact the body.
 2. The fabricating method of the HEMT ofclaim 1, wherein the first III-V compound layer and the third III-Vcompound layer are gallium nitride, and the second III-V compound layercomprises aluminum gallium nitride, aluminum indium nitride, aluminumindium gallium nitride or aluminum indium.
 3. The fabricating method ofthe HEMT of claim 1, wherein the plurality of finger parts are onlydisposed between the body and the drain electrode.
 4. The fabricatingmethod of the HEMT of claim 1, wherein the plurality of finger parts areonly disposed between the body and the source electrode.
 5. Thefabricating method of the HEMT of claim 1, wherein the plurality offinger parts are disposed between the body and the drain electrode, andbetween the body and the source electrode.
 6. The fabricating method ofthe HEMT of claim 1, wherein there is no N-type dopants within theplurality of finger parts.
 7. The fabricating method of the HEMT ofclaim 1, wherein the plurality of finger parts extends along a directionwhich moves away from the body.
 8. A fabricating method of a highelectron mobility transistor (HEMT), comprising: forming a first III-Vcompound layer and a second III-V compound layer, wherein the secondIII-V compound layer is disposed on the first III-V compound layer, anda composition of the first III-V compound layer is different from acomposition of the second III-V compound layer; forming a third III-Vcompound layer disposed on the second III-V compound layer, wherein thethird III-V compound layer comprises a body and a plurality of fingerparts, each of the finger parts is connected to the body, all fingerparts are parallel to each other; and forming a source electrode, adrain electrode and a gate electrode, wherein the source electrode isdisposed at one side of the body, the drain electrode is disposed atanother side of the body and the gate electrode is disposed directly onthe body, wherein steps of forming the third III-V compound layercomprises: forming a P-type III-V compound layer; patterning the P-typeIII-V compound layer to form the body; after forming the body, formingan undoped III-V compound layer covering the second III-V compoundlayer; patterning the undoped III-V compound layer to form the pluralityof finger parts; after forming the body and the plurality of fingerparts, forming a source electrode, a drain electrode and a gateelectrode, wherein the source electrode and the drain electrode contactthe first III-V compound layer, and the gate electrode contacts thebody.
 9. The fabricating method of the HEMT of claim 8, wherein thefirst III-V compound layer and the third III-V compound layer aregallium nitride, and the second III-V compound layer comprises aluminumgallium nitride, aluminum indium nitride, aluminum indium galliumnitride or aluminum indium.
 10. The fabricating method of the HEMT ofclaim 8, wherein the plurality of finger parts are only disposed betweenthe body and the drain electrode.
 11. The fabricating method of the HEMTof claim 8, wherein the plurality of finger parts are only disposedbetween the body and the source electrode.
 12. The fabricating method ofthe HEMT of claim 8, wherein the plurality of finger parts are disposedbetween the body and the drain electrode, and between the body and thesource electrode.
 13. The fabricating method of the HEMT of claim 8,wherein there is no N-type dopants within the plurality of finger parts.14. A fabricating method of a high electron mobility transistor (HEMT),comprising: forming a first III-V compound layer and a second III-Vcompound layer, wherein the second III-V compound layer is disposed onthe first III-V compound layer, and a composition of the first III-Vcompound layer is different from a composition of the second III-Vcompound layer; forming a third III-V compound layer disposed on thesecond III-V compound layer, wherein the third III-V compound layercomprises a body and a plurality of finger parts, each of the fingerparts is connected to the body, all finger parts are parallel to eachother; and forming a source electrode, a drain electrode and a gateelectrode, wherein the source electrode is disposed at one side of thebody, the drain electrode is disposed at another side of the body andthe gate electrode is disposed directly on the body, wherein steps offorming the third III-V compound layer comprises: forming a P-type III-Vcompound layer; patterning the P-type III-V compound layer to form thebody; forming a protective layer covering the body and the second III-Vcompound layer; patterning the first protective layer to form a firstopening which defines predetermined positions of the plurality of fingerparts, wherein the second III-V compound layer is exposed from the firstopening; forming a undoped III-V compound layer filling up the firstopening to form the plurality of finger parts; after forming theplurality of finger parts, patterning the protective layer to form aplurality of second openings respectively defining a predeterminedposition of the source electrode, the drain electrode and the gateelectrode; and forming the source electrode, the drain electrode and thegate electrode to fill in each of the second openings, wherein thesource electrode and the drain electrode contact the first III-Vcompound layer, and the gate electrode contacts the body.
 15. Thefabricating method of the HEMT of claim 14, wherein the first III-Vcompound layer and the third III-V compound layer are gallium nitride,and the second III-V compound layer comprises aluminum gallium nitride,aluminum indium nitride, aluminum indium gallium nitride or aluminumindium.
 16. The fabricating method of the HEMT of claim 14, wherein theplurality of finger parts are only disposed between the body and thedrain electrode.
 17. The fabricating method of the HEMT of claim 14,wherein the plurality of finger parts are only disposed between the bodyand the source electrode.
 18. The fabricating method of the HEMT ofclaim 14, wherein the plurality of finger parts are disposed between thebody and the drain electrode, and between the body and the sourceelectrode.
 19. The fabricating method of the HEMT of claim 14, whereinthere is no N-type dopants within the plurality of finger parts.